The present invention relates to an improvement of a flow rate control valve.
In an automobile, as shown in FIG. 8, a canister 2 containing activated carbon (an absorbent) to absorb evaporated fuel from a fuel tank 1 is connected with the fuel tank 1 through an evaporated fuel passage 3. A flow rate control valve 4 of a diaphragm type which is opened/closed in accordance with an internal pressure of the fuel tank 1 so as to control the flow rate of the evaporated fuel is inserted in the evaporated fuel passage 3. Also, an electromagnetic valve 10 which is closed normally but opened at the time of a diagnostic check is provided in parallel to the flow rate control valve 4.
Normally, the electromagnetic valve 10 is closed. When the tank internal pressure is a preset pressure or higher, a diaphragm 5 is raised against the force of a spring 7, and a valve disk 6 is moved upwardly to open the flow rate control valve 4. When the tank internal pressure is lower than the preset pressure, the valve disk 6 is pressed by the spring 7 and moved downwardly to close the flow rate control valve 4. The portion above the diaphragm 5 communicates with the atmosphere as an atmospheric pressure chamber. The tank internal pressure is exerted on the lower surface of the diaphragm 5.
An inflow port 8 and an outflow port 9 of the flow rate control valve 4 communicate with an upper portion of the fuel tank 1 and a tank port of the, canister 2, respectively.
The electromagnetic valve 10 is opened at the time of a diagnostic check and introduces a negative pressure into the fuel tank 1. In other words, at the time of a diagnostic check, the electromagnetic valve 10 is opened and functions as a bypass passage from the flow rate control valve 4.
A switch valve of a diaphragm type disclosed in Japanese Utility Model Unexamined Publication No. 55-100774 is known as the flow rate control valve (also referred to as a pressure control valve) 4, and a valve disclosed in Japanese Patent Unexamined Publication No. 62-75182, for example, is known as the electromagnetic valve 10.
In the conventional technique described above, the flow rate control valve (also referred to as the pressure control valve) 4 which is opened/closed in accordance with the internal pressure of the fuel tank, and the electromagnetic valve 10 for a bypass disposed in parallel to the flow rate control valve 4, are manufactured to have independent structures of and connected in parallel to each other. Consequently, there arises a first problem that a large space is required for mounting the valves.
Further, in the conventional technique, the valve disk 6 is sometimes adhered on the valve seat by viscous components included in the valve disk 6, or viscous components in a fluid sometimes attach to the valve disk 6 and the valve seat so that the valve will be likewise adhered. As a result, there arises a second problem that the flow rate valve 4 to be operated by the internal pressure in the fuel tank which is a relatively low pressure does not function; that is to say, adhesion of the valve makes it impossible to control the valve with a slight pressure.